An electric power system is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region's homes and businesses with power. For sizable regions, this power system is known as the grid. An electric power system generally includes the generators that supply the power, the transmission system that carries the power from the generating centers to the load centers and the distribution system that feeds the power to nearby homes and industries. Smaller power systems also are found in industry, schools, hospitals, commercial buildings, homes, amusement parks, marine vessels, and the like.
Larger electric power systems also include a grid operator, also known as a transmission system operator or simply as an operator. One function of a grid operator is to manage the security of the power system in real time and to coordinate the supply and demand for electricity. Desirably, the grid operator manages a power system in a manner to avoid undue fluctuations in frequency or interruptions of supply. The grid operator may be an entity that is owned by a transmission grid company or may be fully independent. In some instances, a grid operator is wholly or partly owned by state or national governments. In many cases a grid operator is independent of electricity supplying entities (upstream entities) as well as electricity distribution entities (downstream entities).
The grid operator in many instances works to maintain a continuous (second-by-second) balance between electricity supply from power stations and demand from consumers. The grid operator also may work to ensure the provision of reserves that will allow for safe and timely response to sudden contingencies. The grid operator achieves this by determining an optimal combination of generating stations and reserve providers for each market trading period, instructing generators when and how much electricity to generate, and managing any contingent events that cause the balance between supply and demand to be disrupted. Grid operator staff may undertake this work using sophisticated energy modelling and communications systems.
In some instances, it may be desirable to store electric power for later use. For example, a current availability of electric power supply may be greater than a current demand. If the excess is not stored, it may have to be discarded. In other instances, pricing characteristics of electric power fluctuate. At some times, the price is so low that it is beneficial to store electric power purchased at a low price or even a negative price and then re-supply that power at higher pricing at a subsequent time. In other circumstances, electric consumers may be without power for a period of time due to a power outage. Such outages can be caused by a variety of factors including weather issues and grid problems. In such circumstances, it is desirable to supply stored electric power to users so that their access to electric power is less compromised while grid personnel work to restore the regular power supply.
U.S. Patent Pub. No. 2013/0081394 describes a thermal storage system in which electric energy from an electric power system is thermally stored in molten salt. This innovative thermal storage system is described in context of a solar power system. The solar power is the primary source of thermal energy used to generate electricity. The molten salt is a storage medium used firstly to store electrical energy as thermal energy and secondly to supply thermal energy on demand during periods, such as nighttime or overcast days, when too little solar energy is available.
The thermal storage system proposed by U.S. Patent Pub. No. 2013/0081394 offers great promise as a way to efficiently and cost effectively store electrical energy on a very large scale. However, challenges remain for the system to be constructed more economically. Additionally, the electrical power system that supplies the electrical energy to be stored has characteristics that are constantly changing. A thermal storage system desirably is quickly responsive to these changes when storing electrical energy. A system that responds too slowly might only be able to act in a desired manner only after the conditions leading to a desired action have become obsolete and have been replaced by new conditions that require a different action. A slow system, in other words, is unable to respond to grid changes in a timely fashion.